8300575: JVMTI support when using alternative virtual thread implementation

[backwaterred]

This PR backports modifications to the jvmti code to add support for vthreads. Without this change, we see many failures in our internal testing.

These changes did not apply cleanly in several places because of changes related to JDK-8299837 (Replace NULL with nullptr in hotspot code and tests). In these places, the changes expected code containing nullptr, but found NULL. In these spots, kept the code from the backported change, but changed nullptr back to NULL for consistency with the rest of the code base.

Testing is underway.

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Progress

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Issue

• JDK-8300575: JVMTI support when using alternative virtual thread implementation

Reviewing

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$ git checkout pull/60

Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk20u.git pull/60/head

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$ git pr checkout 60

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[bridgekeeper]

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[openjdk]

This backport pull request has now been updated with issue from the original commit.

[mlbridge]

Webrevs

• 01: Full (f0c71c00)
• 00: Full (19fa8fd7)

[AlanBateman]

Are you sure this is needed JVMTI is optional and a build with the alt implementation doesn't support JVMTI with --enable-preview. So I wouldn't expect you should be running the JVMTI conformance tests with --enable-preview.

[backwaterred]

Things get a bit cryptic when discussing the conformance tests, so feel free to reach out via email if you find my response is not providing the detail you're looking for.

Are you sure this is needed[?] JVMTI is optional...

Basically, yes I'm sure. And, we've received guidance on one of the mailing lists that backporting this change is a possible solution to the difficulty we are facing.

... and a build with the alt implementation doesn't support JVMTI with --enable-preview.

Unless I've misunderstood your comment. Yes, but the changes I'm backporting are meant to enable it.

[AlanBateman]

Things get a bit cryptic when discussing the conformance tests, so feel free to reach out via email if you find my response is not providing the detail you're looking for.

Are you sure this is needed[?] JVMTI is optional...

Basically, yes I'm sure. And, we've received guidance on one of the mailing lists that backporting this change is a possible solution to the difficulty we are facing.

... and a build with the alt implementation doesn't support JVMTI with --enable-preview.

Unless I've misunderstood your comment. Yes, but the changes I'm backporting are meant to enable it.

The changes in JDK-8300575 are not needed in JDK 20u. Not objection to backporting the change but my guess is there is some confusion somewhere that an implementation is required to support JVMTI. JVMTI has always been optional. In this case, JVMTI is not supported in JDK 19/20 when using the alternative implementation of virtual threads and when running with --enable-preview.

[bridgekeeper]

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